Night Lights Cause Breast Cancer While You Sleep 10-14-08

by: David Gutierrez

A lack of darkness at night may increase a woman's risk of developing breast cancer, according to a study conducted by researchers from the University of Haifa, Israel, and published in the journal Chronobiology International.

Researchers used NASA satellite maps to determine how much light was emitted into space from various neighborhoods across Israel at night, which they believed should approximate how bright those neighborhoods are. They then overlaid this map with breast and lung cancer statistics for the same neighborhoods.

As predicted, the researchers found no connection between light levels and lung cancer, but found that women living in neighborhoods with "average" lighting had breast cancer levels 37 percent higher than those living in neighborhoods with low night light levels. Women in communities with the most nighttime lighting had breast cancer rates 64 percent higher than women in communities with the least light.

"By no means are we saying that light at night is the only or the major risk factor for breast cancer," said lead researcher Itai Kloog, "but we found a clear and strong correlation that should be taken into consideration."

Prior research has found higher cancer levels among rats kept in lighted cages at all times, and also among humans who work night shifts. This research has led the World Health Organization to classify night shift work as a "probable carcinogen."

Because lung cancer is caused primarily by smoking, however, researchers believe that the effects of light on the risk of that particular cancer are minimal.

Scientists believe that the carcinogenic effect of night shift work comes with the fact that light prevents the body's production of the tumor-suppressing hormone melatonin, which is normally produced at night. Light in the blue spectrum, such as that emitted by fluorescent bulbs, is particularly damaging to the body's ability to make melatonin.

Supporting this hypothesis is the fact that blind women, who cannot sense light and who have higher than average melatonin levels, have lower breast cancer rates than other women.